1. Field of the Invention
The present invention relates to liquid crystal display devices. More particularly, it relates to an apparatus and method of making three-dimensional (3-D) displays that are capable of viewing a 3-D image.
2. Discussion of the Related Art
In normal vision human eyes perceive views of the world from two different perspectives due to their spatial separation. The spatial separation between typical eyes is about 65 mm. In order to assess the distance between objects, the brain integrates the two perspectives obtained from each eye. In order to provide a display, which is effective in displaying 3-Dimages, it is necessary to recreate this situation to the observer. That is, supplying a so-called “stereoscopic pair” of images to the observer's eyes.
Most 3-D displays may be classified into two types: stereoscopic and autostereoscopic. Stereoscopic displays typically display both of the images over a wide viewing area. The views are encoded by color, polarization state and time of the display. A filter system of glasses worn by the observer separates the views, thereby each eye sees only the view that is intended for it. That is the right and left eyes have different views.
Autostereoscopic displays present a spatial image to the viewer without the use of glasses, goggles or other viewing ads. Instead, the two views are only visible from defined regions of space.
A “viewing region” is a term described as the region of space in which an image is visible across the whole of the display active area. If the observer is situated such that one eye is in one viewing region and the other eye is in the other viewing region, then a correct set of views is seen and a 3D image is perceived by the observer.
In autostereoscopic displays of the “flat panel” type the viewing regions are formed by a combination of the picture element structures (pixels) and optical elements, generically termed a parallax optic. An example of such an optic element is a parallax barrier. This element is a screen with vertical transmissive slits separated by opaque barrier regions.
As a method of displaying the 3-D images without using viewing aids the lenticular method and a parallax barrier method have been conventionally proposed. The lenticular method and the parallax barrier method are stereoscopic image display apparatuses that do not require the use of polarization glasses, shutter glasses, goggles or other viewing ads. In these apparatuses, special optical elements such as lenticular lenses or parallax barriers are generally placed on the front surface sides of display devices. These special optical elements are relatively inexpensive and exhibit high productivity. A simple autostereoscopic image display apparatus can be easily formed by a combination of such an optical elements with a 2D display. Accordingly, these methods are especially suited for use with liquid crystal display devices (LCDs) and the like.
The parallax barrier method is a method in which a parallax barrier comprising an opaque material is slotted with a series of regularly spaced vertical slits and is arranged short of a display screen to cause parallax and to obtain the 3-D images. In the conventional parallax barrier method, a retardation film made of a polymer, a first polarizer and a second polarizer are utilized. Specifically, the retardation film includes a plurality of first regions and a plurality of second regions, these regions are utilized for carrying out an image-splitter method.
FIG. 1A is a global view of a parallax barrier according to a related art, and FIG. 1B is a cross-sectional view of the parallax barrier of FIG. 1A.
The parallax barrier shown in FIGS. 1A and 1B includes a polarization modifying layer 42 and polarizers 44 and 46 in the form of polarizing sheets. The polarization modifying layer 42 includes a patterned retarder layer, which is made by the methods illustrated in FIGS. 2A to 2E. Also, the polarization modifying layer 42 comprises first regions “C” in the form of parallel elongated slit regions. Specifically, these regions are arranged in such a manner to rotate linear polarization of incoming light 41. The first regions “C” are separated by second regions “D” which are arranged not to affect the polarization of the incoming light 41.
The first polarizer 44, which may include the output polarizer of an associated LCD, has a polarizing axis 44a. This axis is oriented at 45 degrees. This is typical of LCD output polarizers, such as the twisted nematic type polarizer. The optic axes of 42a in the first regions “C” are oriented at 90 degrees, and the optic axes 42b of the second regions “D” are aligned at 45 degrees so as to be parallel to the polarization vector of light emitted from the first polarizer 44. The second polarizer 46 has its polarizing axis 46a oriented at 45 degrees. The polarizing axis 46a of the second polarizer 46 is orthogonal to the polarizing axis 44a of the first polarizer 44.
In FIGS. 1A and 1B, when the incident light 41 passes through the first polarizer 44, it is polarized at +45 degrees relative to the vertical axis of the polarization modifying layer 42. The polarization modifying layer 42 has strip-shaped first regions “C” and strip-shaped second regions “D”. The polarization of the light passing through the second regions “D” are not affected, therefore, the second polarizer 46 extinguishes light. This happens because the second polarizer 46 has a polarizing direction indicated at 46a, which is substantially orthogonal to the polarization direction of the light passing through the second regions “D”. After the incident light 41 passes through the first polarizer 44, the polarization of the light passing through the first regions “C” are rotated by 90 degrees and as a result, this light passes through the second polarizer 46. Accordingly, the aforementioned device functions as a parallax barrier.
The polarization modifying layer 40 is made by forming a layer of reactive mesogen, such as RM257, available from MERCK® UK. Utilizing standard photolithographic techniques the layer is then patterned.
FIGS. 2A to 2E are cross-sectional views illustrating the steps of making the polarization modifying layer 40 of FIG. 1A.
In FIG. 2A, a substrate 34 is divided into two regions, a plurality of first regions “C” and a plurality of second regions “D.” Thereafter, an alignment layer 36 is formed on the substrate 34 as shown in FIG. 2B. The alignment layer 36 comprises rubbed polyimide, polyamide, or silicon oxide, which has a first rubbing direction 38a. 
In FIG. 2C, a photo resist 39 is applied to the alignment layer 36 having the first rubbing direction. A mask 40 that has light-transmitting portions “E” and light-shielding portions “F” selectively exposes the photo resist 39. This exposure is accomplished by using known photolithographic techniques. Each of the light-transmitting portions correspond to each of the first regions “C” of the substrate 34, and each of the light-shielding portions correspond to each second regions “D” of the substrate 34. Then the exposed portions of the photo resist 39 associated with the light-transmitting portions “E” are removed, thereby exposing the first regions “C” of the underlying alignment layer 36 as shown in FIG. 2D. Then, the substrate 34 having the alignment layer 36 and photo resist 39 are thermal-heated in a heating apparatus. The substrate assembly is then rubbed in a second rubbing direction 38b in order to produce an alignment layer 37 having a spatially varying alignment direction. As a result, first alignment portions 37a corresponds to each of the first regions “C” having a second rubbing direction 38b, while the second alignment portions 37b corresponds to each of the second region “D” and have the first rubbing direction 38a. 
In FIG. 2E, the residual photo resist 39 of FIG. 2D is then completely removed. A retarder layer 41 is then formed on the alignment layer 37 having first and second alignment portions 37a and 37b. The retarder layer 41 is formed by way of depositing reactive mesogen, such as RM257. The retarder layer 41 adopts the alternate directions imposed by the underlying elements of the alignment layer 37. Namely, the retarder layer 41 has a first direction 38a in the portion corresponding to the second regions “D” and a second direction 38b in the portion corresponding to the first regions “C”.
Alternatively, polyvinyl alcohol (PVA) can be adopted in the above-mentioned slit structure (i.e., the first region “C” of FIG. 1). That is, the polarization modifying layer 42 can be fabricated using the PVA, where a first film causing a first polarization is formed on a first substrate and a second film causing a second polarization state is then formed on a second substrate. Thereafter, the first and second substrates are combined to fabricate the polarization modifying layer and then the parallax barrier. However, this is quite disadvantageous because of the complexity in fabricating the polarization films and the associated increase in the manufacturing costs.
Furthermore, the above method of forming parallel elongated slit regions in the parallax barrier also has disadvantages. As a result of the complexity in the method of manufacturing, the manufacturing yield decreases and the manufacturing cost increases, thereby making this process disadvantageous.